In 2008, the Bureau of Labor Statistics' Census of Fatal Occupational Injuries (CFOI) reported 88 fatalities occurred in the year 2007 related to the use of scaffolds and many more injuries. Twenty-seven percent (27%) of the fatalities and many of the injuries involved falls off of welded frame scaffolds over 25 feet high during the installation of the scaffolds. Safety officials recommend that scaffolding falls be pre-empted through the use of sequential erection techniques. This involves installing guardrails and standards at regular distances along the scaffold such that the exposed platform edge is not greater than a bay length between intervals. The use of safety harnesses or belts tethered to guardrails during the erection process is also a recommended safety practice. However, the use of safety harnesses to deter fall injuries during scaffold erection is quite limited due to the components used in conventional scaffolds. The nature and design of conventional scaffold components, as described herein, disadvantageously do not allow the effective use of safety harnesses during the erection process.
Tube and coupler scaffolds are so-named because they are built from tubing connected by coupling devices. Due to their strength, they are frequently used where heavy loads need to be carried, or where multiple platforms must reach several stories high. Components of scaffolds include vertical standards having coupling rings or rosettes, horizontal components such as ledgers and guardrails coupled to the coupling rings or rosettes, footings, decks/platforms and diagonal braces. Their versatility, which enables them to be assembled in multiple directions in a variety of settings, also makes them difficult to build correctly.
Conventional scaffolding systems have various components. FIG. 1 illustrates a supported scaffold 100 consisting of one or more platforms supported by rigid support members such as poles, tubes, beams, brackets, posts, frames and the like. More specifically, the supported scaffold 100 includes the following components: deck/platform 101, horizontal members, or ledgers 102, and vertical standards 103. Additional components include diagonal braces to increase the stiffness and rigidity of the scaffold 100.
FIG. 2 is an illustration of a vertical standard 103. Vertical standards are typically cylindrical tubes 200 comprised of hot-dip galvanized steel or aluminum. A collar with an expanded or reduced diameter or a spigot at either or both ends of the vertical standard facilitates the joining of vertical standards from end to end. Rosettes 201 are positioned and then welded or otherwise attached along the tubes providing connections for horizontal members and diagonal braces. The vertical standard can have from one to 8 or more rosettes placed along the tubing using a predetermined spacing between rosettes, for example, about every 20 inches.
FIG. 3 illustrates a ledger 102. A ledger is a horizontal member that serves as both a guardrail and bracing element. The ledger 102 is comprised of tubing 300, heads 301 and wedges 302. Ledgers 102 are available in different lengths, depending on the scaffolding bay length, deck type and load. It is the conventional manner in which these ledgers are coupled to vertical standards that contribute to scaffolding falls as further described herein. Once the tubing on a level is installed, decks or platforms 101 made of, e.g., hot-dip galvanized steel, aluminum, wood or an aluminum frame with plywood board are installed to allow workers to traverse the scaffold 100 and install the guardrails (e.g., ledgers 102).
Referring now to FIG. 4, wedge 302 is shown being hammered into the slot or gap of head 301 at the end of a ledger 102 so as to couple it to the rosette 201 of the vertical standard 200. This must be done by a worker first at the proximate end of the ledger 102 and then at the distal end of the ledger 102. However, as the proximate end of the ledger 102 is being coupled to the vertical standard using the wedge 302, the distal end of the ledger 102 is free and uncoupled, that is, until the worker can traverse the platform to the distal end of the ledger 102 and hammer in a wedge 302 at the distal end. During this time, the distal end of the ledger 102 remains uncoupled from the vertical standard. Hence, if the installer is harnessed to the ledger 102 and the scaffold tilts toward the uncoupled, distal end, the installer may tumble down the platform and the safety harness will exit the uncoupled end of the ledger, providing no measure of safety to the installer.
A conventional rosette 500, as seen in FIG. 10, has a central aperture 503 to receive the vertical tubing, four small openings 501 A-D to facilitate right-angled connections and four larger openings 502 A-D to facilitate connections at any angles. Typically, a vertically and horizontally slotted head 504 coupled to the end of a ledger is positioned with respect to the rosette 500 such that the horizontal slot of the head 504 is positioned over and under the rosette 500 and the vertical slot of the head is aligned with an aperture of the rosette 500. A wedge 302 is then hammered into the vertical slot (or gap) to couple the ledger 102 via the head 504 to the vertical standard 103 via the rosette 500 using, inter alia, frictional force. Note that, disadvantageously, until the wedge 302 is installed, there is significant play between the rosette 500 and head of a horizontal member giving rise to safety concerns. Furthermore, once installed, wedges often work free when workers traverse the platform. When these wedges work free, the scaffold can become unstable and collapse. Further, even if the scaffold does not collapse, steel wedges, which, as seen in the Figure, are not integrated into the head or the ledger, can fall from the scaffold injuring workers below.
Another type of modular scaffold joint uses an end connector positioned on the end of a horizontal member, where the end connector has a lip or hook section that is designed to engage or rest on a corresponding vertical connector cup or annular ring positioned on a vertical scaffold member. One such joint is disclosed in U.S. Pat. No. 4,445,307 (the Safway system scaffold) which discloses a connector 1000 positioned on a horizontal scaffold member 1001, where the connector has two vertically spaced hook sections 1003. An example of the Safway joint is shown in FIG. 5. These hook sections couple with two vertically spaced upstanding cup ring members 1102 located on the vertical scaffold member 1100. Each cup member has a surrounding annular lip 1103 to which the hook members on a horizontal member end connector engage. To lock the joint in place, the connector includes a wedge 1005 that is driven (generally by a hammer) into position below or on the underside of the lower cup member, thereby wedging the cup 1102 against the end connector hood section 1003, latching the horizontal member to the vertical member. As used herein, “latching” refers to the action of engaging a horizontal member to a vertical member, where the action of latching resists dislodgement of the horizontal member from the vertical member from an upwardly directed force.
Another cup type of latching connector is disclosed in U.S. Pat. Nos. 5,078,532 and 5,028,164 and in U.S. application Ser. No. 12/489,166, all hereby incorporated by reference (the Excel system scaffold). One embodiment of an Excel-type end connector is shown in FIG. 6. These patents and applications also have an end connector 2000 positioned on a horizontal scaffold member 2001, where the connector has two vertically spaced hooked sections 2003 that couple with two vertically spaced upstanding cup members 2102 located on the vertical scaffold member 2100. Each cup member 2102 has a terminating edge or lip section 2103 that is used to engage the hook sections 2003 on the horizontal end connector 2000. In this device, the hooked sections 2003 engage the top edge of the cup 2103, and a pivoting member or latch 2003, positioned on the horizontal end connector, is pivoted into position below the top cup member. The latch member 2003 has a distal end extending beyond the housing toward the vertical member, shaped to allow for placement of the distal end beneath a cup 2102 positioned on a vertical scaffold member. Hence, when latched, the cup 2102 is trapped between the hook engagement sections 2003 of the connector housing and the distal end of the latch member 2003. The latch pivots on a pivot pin, and can be spring loaded to bias the latch into a locking or actuated position. The latch is operated by trigger or handle 2004. Single cup embodiments are also possible, such as shown in U.S. Pat. No. 7,048,093 (hereby incorporated by reference).
What is desired is a scaffolding apparatus that is configured to couple each end of a horizontal scaffold member (also referred to herein as a horizontal, or horizontal member or a ledger) to a vertical standard (also referred to herein as a vertical member, vertical or vertical scaffold member), where the vertical member has upstanding cups, and an assembly mechanism that allows a single installer to insert and lock pivoting wedges at both ends of the horizontal member, and to release both ends substantially simultaneously if using the primary trigger, or to only release one end if using the secondary trigger.